Use of an unmanned police car to reduce traffic speed

Objective: Motor vehicle collisions are the most common mechanism of trauma tic death. Speeding is often implicated as a causal factor in motor vehicle crashes. One potential intervention, to prevent speeding, is the placement of a roadside unmanned police car. This study sought to answer the followi ng questions: is speeding reduced by this intervention, does this intervent ion lose effectiveness over time, and when the car is removed, do motorists resume speeding? Methods: A radarless speed detector was placed on a roadway that had a hist ory of speed-related collisions. Baseline speeds were recorded for 12 days. Thereafter, an unmanned police cruiser was parked near the road, and speed s were recorded for 10 days. The police car was removed, and data collectio n continued 1 more week. The difference between the proportion of motorists exceeding 45-mph in the baseline period and the decoy intervention period was tested by using a chi(2) test. Results: During the baseline surveillance, 72.0% of vehicles (186,578 of 25 9,074 motorists) had speeds greater than 45 mph. After placement of the unm anned police car, 41.0% of motorists (92,272 of 225,026 motorists) exceeded 45 mph (p <.0001). Over the 10-day study period, when the decoy police car was in place, the percentage of motorists exceeding 45 mph gradually incre ased from 27.2% to 47.4%. Upon removal of the police car, speeding returned approximately to baseline, with 67.5% of motorists (120,640 of 178,752 mot orists) exceeding 45-mph. Conclusion: Parking an unmanned police car beside a road was associated wit h a large reduction in speeding over a 10-day period. Removal of the unmann ed police car resulted in a return to preintervention speeding.